Adding a contribution replaces some existing data, in specific case?

**Describe the bug**

I asked the bot to add me as a `maintenance` contributor in a repo that had been pre-populated with a table. It removed my two existing contributions -`tool`, `design`- in the process.

**To Reproduce**

1. See this comment: https://github.com/JoshuaKGoldberg/tidelift-me-up-site/issues/8#issuecomment-1624086542
2. See this PR: https://github.com/JoshuaKGoldberg/tidelift-me-up-site/pull/13

**Expected behavior**
Don't delete existing contribution types? Or if they're invalid in some way _(are they?)_, mention that somewhere?

**Additional context**

This _might_ be the reproduction for https://github.com/all-contributors/cli/issues/355, finally? fyi @Berkmann18

Edit: it seems to be happening reliably on that repo. https://github.com/JoshuaKGoldberg/tidelift-me-up-site/pull/56#issuecomment-1694663582 -> https://github.com/JoshuaKGoldberg/tidelift-me-up-site/pull/58

Edit: and also here! https://github.com/JoshuaKGoldberg/refined-saved-replies/pull/172